915 Rebuild

[Coultl]

Taking a break on the turbo system design HERE and tacking the trans rebuild.

After draining $100 worth of Swepco out, I tore everything down tonight and found the pinion bearing spinning in the case and both bearing races spinning in the gear housing. Crap.

Also, this trans shifted terribly, lots of grinding and 2nd and 3rd. On inspection I don’t see crazy wear on the dog teeth but they are not razor sharp either. The synchro bands show some wear but they still mostly have their texture.

The engine is going to get a turbo so I will be using a Wevo side cover and CMS bearing plate to add a little strength.

A couple of questions if anyone has thoughts:

- Thinking I’ll go to CMS to get the case machined. They seem to have a good reputation. Honestly, if I’m sending it there I might just have them do the entire rebuild.

- Does Carquip in Boulder do machine work? Seems like maybe they are only parts now. Any other good places to get the case work done?

- Any experience with particular brand replacement parts (synchro and dog teeth)?

- What do worn dog teeth look like? How rounded is too rounded?

[Coultl]

Here are some photos of 2nd and 3d synchros and dog teeth.

Also, is the profile of my 1st gear normal. It’s for a bit of a dimple on the outer edge of the teeth. It’s uniform / on all teeth.

Thanks in advance!

[Tonger]

I would actively avoid Carquip. They rebuilt a 915 for me and the bill was extremely high. The other problem is that it had to be sent back x2 because of build problems. In the end, we gave up on them and had it completed elsewhere. The whole experience was very poor and it was a hugely expensive mistake to use them.

CMS is terrific. They do great work and have high standards.

I would also suggest Mark Epstein (mepstein on the forum). Although he hasn't built a transmission for me I have done business with him and he is a very straight shooter.

Best of luck

[mepstein]

Thank you Tonger
We build a lot of transmissions
We send the cases to CMS for machining. They do great work.

[yelcab1]

You are in Colorado, if you are gonna send it anywhere, I heard John Walker does good work.

[Matt Monson]

Carquip definitely doesn’t do that kind of work anymore. They haven’t had a good builder in a decade or more. In recent years they’ve used SAS, next door but I recently read about several people suing SAS to get their cars back. No idea what’s going on, but I’d avoid it.

Unfortunately there’s no local case machine work here in CO. Send it to CMS.

[Aztim]

Aztransaxle in phx is top notch

Hes doing mine right now, approx 4k including a Patrick sidecover and bearing plate

[Jdub]

Second the advice to send to John Walker. He rebuilt my 915 and his work is based on experience and honesty. When the Goetze rings he used across a set of builds were questionable he notified his customers and rebuilt every transmission. That is service.

[Coultl]

Thank you so much for all the leads. VERY helpful. Now, I just need to figure out the right combo of pro help and DIY to keep me from going broke!

[yelcab1]

Originally Posted by Jdub

...When the Goetze rings [JW] used across a set of builds were questionable he notified his customers and rebuilt every transmission. That is service.

It's how you handle the bad situations that defines who you are!

[kevingross]

Getting back to your photos, the dimple on 1st gear is normal.

Your synchros are heavily worn and should be replaced, along with their mating shift sleeves. Your dog teeth do not look horrible, although I see some wear to some of their tips. Be sure to measure the installed diameter of your new synchros to confirm that the dog rings are not excessively worn -- this is the other important thing to check on them. I recommend (and use) a C-clamp type micrometer at 90 degrees out from the gap in the synchro, rather than a sliding bar type mic. Good luck with the project!

[acj47]

@Coultl, I'm located in Fort Collins and planning to get my 915 rebuilt over the winter, so please let us know what/who you decide to go with and how it goes!

[Matt Monson]

Originally Posted by acj47

@Coultl, I'm located in Fort Collins and planning to get my 915 rebuilt over the winter, so please let us know what/who you decide to go with and how it goes!

Poudre Sports Car. They can ship it out for repairs if they get into it and it needs case work.

[acj47]

Originally Posted by Matt Monson

Poudre Sports Car. They can ship it out for repairs if they get into it and it needs case work.

thanks - Zach @ Poudre Sports Car is definitely on the list!

[acj47]

are the billet side cover (ex. CMS or Wevo) and bearing retaining plate considered 'must-do' upgrades for a 915 rebuild? any reason not to spend a little more $ for them?

[kevingross]

Originally Posted by acj47

are the billet side cover (ex. CMS or Wevo) and bearing retaining plate considered 'must-do' upgrades for a 915 rebuild? any reason not to spend a little more $ for them?

I consider the one-piece bearing plate a "must do." Guard, CMS, and Wevo all make them.

The billet side cover is a bit more situational, but it's never a bad idea. Certainly if you have a magnesium case, and especially if it has corroded around the steel fasteners.

[Coultl]

Good call. I do have a CMS one-piece bearing retainer and a Wevo side cover. This car will have some boost but I'll tune it to keep torque below 350 lbft...closer to 300 lbft.

[Coultl]

My first gear is looking pretty worn and I'm thinking about getting a weld on replacement:

https://retro-sport.com/porsche-gears/porsche-915-gears/porsche-915-1st-gears

I think the 14:39 ratio is a good option. It's a good bit taller than stock.

Bill Verburg, if you happen to be around, I'd love to get your perspective on how this would change the feel and see the speed vs. rpm graphs. The engine redline will be 7,500 and the rear tire size is 225/50/R16.

My hope is that this longer range would keep my in boost (keep rpm from dropping below 4k) from 1st to 2nd.

Open to any and all feedback!

[Coultl]

I did a little digging and I see some pros and cons to the taller 1st gear. This car should come into boost at about 3500 rpm. The taller first gear will hit 3500 rpm 3 mph higher (24mph vs. 21mph). It's going to feel a little more laggy in 1st gear.

Put another way, the rpm will be 500 lower at 24mph with the taller 1st gear.

On the plus side, it will be much easier to say in boost when shifting to second. The only Porsche I can find with a 1st gear this tall is the 964 Turbo. (The 993 and 930 turbo both have similar 1st gears when you account for the changes in the final drive ratio)

So, not an easy call without actually driving it. I could argue either way!

[john walker's workshop]

1st in a 915 is over in an instant with a turbo engine. Maybe find a 930 box, for all the $$$ you will spend on your 915. Way beefier. I would be hesitant to warranty a 915 with a turbo engine abusing it.